Toto Wolff says it is "just a matter of time" until Lewis Hamilton signs a contract extension to keep him at Mercedes beyond 2018.

The reigning world champion has entered the final year of his contract but has been in talks about a new deal for some time. At the end of last season, Wolff told ESPN he doubted Hamilton would leave Mercedes unexpectedly, as Nico Rosberg did after winning the 2016 world championship, and it seems the discussions have continued down an encouraging path.

"Lewis has become such an important pillar within the team, it is a no-brainer that we continue with each other," Wolff told Mercedes' official website. "The discussions are ongoing and with a very positive mind-set. It is just a matter of time, when we seal it and put the signature to the document."

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Since signing with Mercedes in 2013, Hamilton has enjoyed one of the most dominant spells of any driver in F1 history, claiming three of his four world titles and becoming the sport's leader in career pole positions. Mercedes hopes to continue that dominance into 2018, but also enters the new campaign knowing its other driver, Valtteri Bottas, is entering a contract year of his own.

Bottas' future is much less certain: the Finn was retained on a one-year extension after a mixed debut season with the team. With the likes of Daniel Ricciardo available and Mercedes junior Esteban Ocon continuing to impress, the German manufacturer is likely to have a wide array of options.

Speaking about Mercedes' current set of junior drivers, Wolff explained his expectations: "Every year, we set objectives for the boys and they have matched those objectives last year. The bar is rising. If you want to qualify for a Mercedes, you need to be quick, make no mistakes, work well within your team, be respected by your team and energise your team. All of these factors that we try to capture and measure. We will see where they end up in a years' time."